Wiring Help Needed... 240volt 15amp Compressor??

[EL1NOR]

Hi,
I just bought a new craftsman air compressor for my garage and it requires 240volts at 15amps. I have yet to wire the garage for 240, so I'm SOL at the moment. My plans right now are to use my 240volt 30amp generator to supply the power in the meantime.

Problem:
-The generator has a 4-prong 240volt/20amp plug outlet on it.
-The compressor has a 3-wire setup inside the pressure switch box.

I went and bought a small circuit breaker panel box for the garage and a dual 15amp breaker for the compressor. I'm confused with the wiring now because I know from the generator I'd need a 4-pronged plug with the black(power), red(power), white(neutral), and green(ground) wires in it. So I'd have to buy a long cord to go from the plug I put in the generator, hardwired into the circuit breaker box. So all I'd have to do is start the generator and plug the wire into it to bring power to the breaker.

But how do I go about wiring it from the breaker to the compressor now?? I've got 4 wires going in and only 3 wires going out to the compressor? Huh?! How can I get 240volts at 15amps in a single phase setup? Am I supposed to run the 4 wires out of the breaker box and then just connect the black and red wires while wiring the compressor??

Basically, everything will be hard-wired except for the generator. 4 wires in and 3 wires out??

Lost,
-Tim

 

[Ozsum2]

Hi,
I just bought a new craftsman air compressor for my garage and it requires 240volts at 15amps. I have yet to wire the garage for 240, so I'm SOL at the moment. My plans right now are to use my 240volt 30amp generator to supply the power in the meantime.

Problem:
-The generator has a 4-prong 240volt/20amp plug outlet on it.
-The compressor has a 3-wire setup inside the pressure switch box.

I went and bought a small circuit breaker panel box for the garage and a dual 15amp breaker for the compressor. I'm confused with the wiring now because I know from the generator I'd need a 4-pronged plug with the black(power), red(power), white(neutral), and green(ground) wires in it. So I'd have to buy a long cord to go from the plug I put in the generator, hardwired into the circuit breaker box. So all I'd have to do is start the generator and plug the wire into it to bring power to the breaker.

But how do I go about wiring it from the breaker to the compressor now?? I've got 4 wires going in and only 3 wires going out to the compressor? Huh?! How can I get 240volts at 15amps in a single phase setup? Am I supposed to run the 4 wires out of the breaker box and then just connect the black and red wires while wiring the compressor??

Basically, everything will be hard-wired except for the generator. 4 wires in and 3 wires out??

Lost,
-Tim

It's been 12 years since I wired my house, but can't the neutral be the ground as well?

 

[1320stang]

My 60 gal. upright direct drive 6hp 240v compressor had contacts for 4 wires. I bought it used so I had to get a plug for it. Got a dryer plug that matched the plug for my dryer outlet. Eventually I hard wired it on the dryer circuit (rental house) but thats a long story.

I don't know how big the compressor you bought is, but if its the full upright and you bought the oil free one, you'll be happier in the long run if you spend the few extra dollars and get the cast iron oil bath one. I got rid of mine. Getting a twin cylinder cast iron one soon. 15.1 SCFM 2 90 psi WOOT!!!

 

[WORTH]

The neutral and the ground connect to the same BAR in the panel box. So you really only have 3 wires.

red/black are our 2 power wires and the white will be nuetral.

I'm a bit confused though, why are you wiring the generator to a panel?Is this a remote building?

 

[Ozsum2]

The neutral and the ground connect to the same BAR in the panel box. So you really only have 3 wires.

red/black are our 2 power wires and the white will be nuetral.

I'm a bit confused though, why are you wiring the generator to a panel?Is this a remote building?

I thought that is the way I remembered it. There was a ground wire coming off the neatral block going to the ground rod in the soil. There is just 3 wires coming in off the pole. 2 hot and 1 ground.

 

[WORTH]

I thought that is the way I remembered it. There was a ground wire coming off the neatral block going to the ground rod in the soil. There is just 3 wires coming in off the pole. 2 hot and 1 ground.

The only time I have ever seen the ground and the neutral seperate is in a SUB-PANEL, but when it gets back to the main panel they are back together again, So I have no idea why they do it that way.

 

[nosaj122081]

The only time I have ever seen the ground and the neutral seperate is in a SUB-PANEL, but when it gets back to the main panel they are back together again, So I have no idea why they do it that way.

If you've ever had the JOY of farting around with wiring in an old house, sometimes they left the neutral floating for some god-forsaken reason, making it ALOT of fun to work on. The house I live in now I need to connect the bars in the box, the neutral is floating .

 

[limey66]

I think I might be able to help out here, but I'll need to check back once I've checked out my reference books at work...

I'm an electrical engineer, and I do a lot of work for your airmen and women that are stationed over here in the UK, so I kinda know how your crazy US power works, but I mainly do the 120V single phase stuff for running PCs and stuff.

I think I'm right that a standard domestic supply in the US is two phases (240V line to line) with a neutral and an earth (or ground). Around the house you have any one phase and a neutral which gives you 120V line to neutral (and a grounding wire of course). Then I think you have a dryer outlet that has the two phases and a neutral with ground.

Your compressor (I'm guessing here, but a look in the manual should confirm this) is a two phase machine, which means it doesn't need a neutral, just the two 'hot' lines and the ground to connect to it which gives you your three wires. Your generator has a neutral connection because you might need it for single phase equipment, but I think you can just leave it unconnected for this application.

I might be talking absolute crap here (eh, WORTH?), but I'll hit the books when I get to work in the morning and report back.

 

[EL1NOR]

Thanks for the replies.. this should explain better.

My house has the main circuit breaker panel in the basement. All the breakers are used up. It also has a sub-panel installed right next to it. The sub-panel is an INPUT PANEL for our generator in case we lose power in the winter. The INPUT sub-panel doesn't have the garage on any of the breakers, just main ammenities.

My garage isn't wired for 240V, only 120V.

I just bought this compressor:

http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=TOOL&pid=00918419000

-The manual says that the compressor requires 240V @ 15amps.

-Our generator dishes out 240V @ 30amps.

So I decided that I could install a small circuit breaker panel in the garage, separate from the house. It has 1 dual 15amp breaker on it (for the 240V compressor) and 2 separate 15amp breakers for other garage ammenities I may need to use during a storm.

The problem I have is that the compressor has only 3 wires on it:

1 is green and that is the ground wire.
1 is black and that is the hot wire.
1 is white and that is the neutral wire.

I'm confused as to how I'm supposed to get 240V of electricity into the compressor with only the black wire. Typically it's a black wire and a red wire, both which are hot 120V lines, that deliver the combined total of 240V.

If that isn't confusing enough, my generator's plug receptacle is a 4-prong. It requires a 4-wire system (black, RED, white, green). The system would be like this:

generator..... plug+wire ...... breaker..... compressor
[ ] =[]--------------------------| |---------------[ ]

With power going this way across the system: --------->

So I suppose my MAIN QUESTION is "how do I wire up the compressor itself? Regardless of the rest of the system...."

-Tim

 

[Ozsum2]

You are going to need to study the schematics of the comp. wiring. In some cases, the motor can be hooked up to either 110 or 220 by deleting a wire or using all. You need to determine which wires can achieve you the 220. Basiacally, you need 2 hot and 1 ground. And the 2 hot need to be from seperate sources. If not you still just have 110.

 

[EL1NOR]

Craftsman is terrible. There isn't a schematic or any details on the wiring. Simply "A proffessional electrician is required to install".

Being politically correct and covering ones' ass is very popular in this century.

I was thinking that maybe their idea is to have no neutral and just 2 hots and a ground. But then I questioned "then why the hell is it WHITE and black. White has always been known as neutral". So now I'm questioning if I should just use my 4-wire system, but connect the black AND THE RED to the black terminal on the compressor to supply the 240V and still put the white with the white for neutral and the green with the green for ground.

I'm not ready to risk it though. This sucks,
-Tim

 

[Ozsum2]

Craftsman is terrible. There isn't a schematic or any details on the wiring. Simply "A proffessional electrician is required to install".

Being politically correct and covering ones' ass is very popular in this century.

I was thinking that maybe their idea is to have no neutral and just 2 hots and a ground. But then I questioned "then why the hell is it WHITE and black. White has always been known as neutral". So now I'm questioning if I should just use my 4-wire system, but connect the black AND THE RED to the black terminal on the compressor to supply the 240V and still put the white with the white for neutral and the green with the green for ground.

I'm not ready to risk it though. This sucks,
-Tim

No, white can be hot too like on a 3 way wall switch. Green is just about always ground. Call Crftsman. They can help. I'd hate you to burn it up by putting the red and black on 1 wire.

 

[nosaj122081]

limey66,
I'm pretty sure our houses here run off a single 120V/240V phase of a 3 phase center-tapped delta from the pole. I remember this b/c when I took my AC Machinery & Controls class, I thought the same thing you said when we began discussing 3 phase, that our houses got 2 120V phases, but about as soon as I thought it up my professor shot it down and explained that we just get a center-tapped single stage. Theres 3 phases running on the pole but what each house gets is just one leg of it.

As far as the compressor wiring, can you remove the cord from the compressor, like you can a dryer or a range? If so, I would do that, go and buy a 4 prong cord for it, the new white wire would connect to the compressors neutral, then bolt the green somewhere to the compressor for the ground. This is the best way IMHO, you're wiring is up to code with the 4 prong outlet, the 3 prong outlets aren't up to code anymore for new constructions. I may be confused on what you're saying though.

I'm no electrician though, my Dad was and I just regurgitate what he told me... I'm just a EE student, which on the food chain is pretty dang low, LOL.

 

[nosaj122081]

No, white can be hot too like on a 3 way wall switch. Green is just about always ground. Call Crftsman. They can help. I'd hate you to burn it up by putting the red and black on 1 wire.

Switches are a different story, but the white should ALWAYS be common, black hot for outlets and such... Reverse it and you run the risk of having the hot connected to whatever tool/appliance/etc.'s chassis. Thats why we have polarized plugs now.

 

[Ozsum2]

Switches are a different story, but the white should ALWAYS be common, black hot for outlets and such... Reverse it and you run the risk of having the hot connected to whatever tool/appliance/etc.'s chassis. Thats why we have polarized plugs now.

Yea, I know switches can be different, but explain how he gets 220 with only 1 hot wire? I guess if it came off the main before it gets split up going down to the curcuits.

 

[nosaj122081]

Yea, I know switches can be different, but explain how he gets 220 with only 1 hot wire? I guess if it came off the main before it gets split up going down to the curcuits.

If you measure between black and red, it should be 240V, from black to white or from red to white should be 120V. In things like a dryer or a range, there are 120V components and 240V components. The common and the ground used the same line in a 3 line setup.

 

[EL1NOR]

... and just so everyone knows... the compressor doesn't have a cord. It didn't come with one or anything. You have to wire in your own inside the switch box on the compressor. Inside is the terminal setup I explained earlier. The green is definitely grounded.... then the white and black are on (obviously) 2 separate terminals. When you throw the switch on the compressor to "ON", it simply connects the white and the black posts. That sounds more like a 120V setup than a 240V.

Craftsman sucks sometimes,
-Tim

 

[Ronstang]

This is rather simple Tim and you are looking too hard for an answer. The white and black wires are each hot and should each get connected to a 120V hot source from one side of a double throw 240V breaker. You can bridge the neutrals and hook them to the green wire as it is the ground or return. I usually tap into the dryer circuit and piggyback the compressor off of that circuit since I don't need to run both at the same time. If your garage is detached from the house and has two separate 120V circuits run to it you can install a smalll breaker box that allows you to use those 2 circuits to create a 240V circuit for the garage with a dual throw breaker for protection....this is not to code but will work and be safe as long as you install the 240V breaker.

 

[nosaj122081]

... and just so everyone knows... the compressor doesn't have a cord. It didn't come with one or anything. You have to wire in your own inside the switch box on the compressor. Inside is the terminal setup I explained earlier. The green is definitely grounded.... then the white and black are on (obviously) 2 separate terminals. When you throw the switch on the compressor to "ON", it simply connects the white and the black posts. That sounds more like a 120V setup than a 240V.

Craftsman sucks sometimes,
-Tim

See my last post for an answer to that... You don't need any 120V line in a compressor, just 240V, so it sounds like they ditched the center-tap line... When we're talking about voltage, we're talkign about the DIFFERENCE in potential. So if you were to measure the voltage from the 240V line to the 120V line, it would read 120V, as would 120V to ground. Sounds like you just need the 240V hot, ground, and common.

White should never be hot in a situation like this... Its dangerous... It would put a potential on the chassis of the compressor.

 

[limey66]

limey66,
I'm pretty sure our houses here run off a single 120V/240V phase of a 3 phase center-tapped delta from the pole. I remember this b/c when I took my AC Machinery & Controls class, I thought the same thing you said when we began discussing 3 phase, that our houses got 2 120V phases, but about as soon as I thought it up my professor shot it down and explained that we just get a center-tapped single stage. Theres 3 phases running on the pole but what each house gets is just one leg of it....

I'll pull out my copy of the NEC when I get to work in the morning (you guys will be all tucked up in bed...) Just don't do anything until we know what's going on here.

Surely there must be an American electrician on the Forum somewhere?